The following correction was printed in the Guardian's Corrections and clarifications column, Wednesday October 25 2006

Weber Shandwick have asked us to make clear that they were not involved in making a campaign video for Cancer United decribed in the article below.

A Labour MP who chairs the all-party parliamentary group on cancer said last night that he had been "naive" to get involved with Cancer United, a pan-European campaign mired in controversy over drug company sponsorship.

Ian Gibson, a former chair of the science and technology select committee, was invited to be filmed for the launch of the campaign during the Labour conference in Manchester.

"They had taken rooms in a hotel," he said. "They invited people to come and say some positive things about the issue on camera. I said who had they got and they said they had other celebrities, like Alastair Campbell."

Mr Campbell, the prime minister's former spokesman, said he was "upset" he had become involved.

Dr Gibson said he understood the campaign was about equal access to cancer treatment across Europe, but he did not know the sole funder was Roche, the world's biggest manufacturer of cancer drugs, until the Guardian revealed it on Wednesday.

The campaign's secretariat is Weber Shandwick, Roche's PR company in Brussels, and a senior Roche official sits on the campaign's executive board.

Mr Campbell, the former Downing Street press secretary, recorded an interview in support of the campaign when he was approached several months ago.

"I thought it was a European Union campaign on cancer awareness," said Mr Campbell, a long-standing supporter of research in the fight against leukaemia.

"I'm more upset because I thought I had an agreement I would be able to use it to promote work on leukaemia research but that appears not to be the case."

Pre-launch publicity indicated the campaign would rely heavily on a report from the Karolinska Institute, Stockholm, which claimed that cancer survival was linked to a country's spending on drugs - and which was also funded by Roche.

An MEP and the head of the European Cancer Patients Coalition, the Guardian revealed, have withdrawn from the campaign's executive board over concerns about its independence and lack of transparency over its funding.

Dr Gibson says he has now pulled out of any involvement. "I feel very silly and stupid," he said.

At the sparsely attended campaign launch in Brussels yesterday, Cancer United said the aim was to promote equal access to the best forms of cancer care across the EU's 25 countries and denied that it was the plaything of a commercial exercise. Campaign leaders also rejected accusations that its sole aim was to lobby EU institutions and national governments for more money to combat cancer.

The campaign admitted the funding from Roche, which makes Herceptin for breast cancer and Avastin for bowel cancer, and "logistical support" from Weber Shandwick. But John Smyth, the campaign's chairman and professor of medical oncology at Edinburgh University, said Roche had simply paid for two visits of 12 board members to Brussels.

On BBC Radio 4's Today, Professor Michel Coleman from the London School of Hygiene and Tropical Medicine criticised the Karolinska report, which claimed cancer survival was directly linked to a country's spending on drugs. "The research on which Cancer United is being launched is faulty," Prof Coleman said. One of its major failings was that it matched drug availability against survival data for patients from a period up to 10 years earlier.